<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>
<script>
  let user = {};
  let hd = user;
  //  user hd  指向了同一个内存地址，对象是传递地址， 值类型是传递值本身

</script>
</body>
</html>